streams: Pass stream_weekly_traffic field in stream objects.

This commit adds code to pass stream traffic data using
the "stream_weekly_traffic" field in stream objects.

We already include the traffic data in Subscription objects,
but the traffic data does not depend on the user to stream
relationship and is stream-only information, so it's better
to include it in Stream objects. We may remove the traffic
data and other stream information fields for Subscription
objects in future.

This will help clients to correctly display the stream
traffic data in case where client receives a stream
creation event and no subscription event, for an already
existing stream which the user did not have access to before.

zerver/views/streams.py

@@ -58,6 +58,7 @@ from zerver.lib.request import REQ, has_request_variables
 from zerver.lib.response import json_partial_success, json_success
 from zerver.lib.retention import STREAM_MESSAGE_BATCH_SIZE as RETENTION_STREAM_MESSAGE_BATCH_SIZE
 from zerver.lib.retention import parse_message_retention_days
+from zerver.lib.stream_traffic import get_streams_traffic
 from zerver.lib.streams import (
     StreamDict,
     access_default_stream_group_by_id,
@@ -874,7 +875,12 @@ def get_stream_backend(
     stream_id: int,
 ) -> HttpResponse:
     (stream, sub) = access_stream_by_id(user_profile, stream_id, allow_realm_admin=True)
-    return json_success(request, data={"stream": stream_to_dict(stream)})
+
+    recent_traffic = None
+    if not user_profile.realm.is_zephyr_mirror_realm:
+        # We do not need stream traffic data in zephyr mirroring realm.
+        recent_traffic = get_streams_traffic({stream.id})
+    return json_success(request, data={"stream": stream_to_dict(stream, recent_traffic)})
 
 
 @has_request_variables